1. Field of the Invention
This invention relates to a liquid chromatograph including a mobile phase supplying apparatus of a high-pressure gradient system, the mobile phase supplying apparatus supplying mobile phases while controlling a composition of the mobile phases, the mobile phase supplying apparatus having a plurality of liquid-feeding pumps for feeding the mobile phases, respectively, a plurality of liquid-feeding flow paths having the liquid-feeding pumps, respectively, a mixer for mixing the mobile phases by merging the liquid-feeding flow paths; at least one control device for controlling a driving of each of the liquid-feeding pumps based on a flow rate being set. This invention also relates to a liquid chromatograph including a high-speed liquid chromatograph using the mobile phase supplying apparatus. This invention also relates to a mobile phase supplying method in the liquid chromatograph including the mobile phase supplying apparatus.
2. Description of the Related Art
FIG. 4 shows a liquid chromatograph equipped with a related mobile phase supplying apparatus of a high-pressure gradient system.
Liquid-feeding pumps 10, 14 are provided respectively in liquid-feeding flow paths 2, 4 for feeding mobile phases A, B. Each of the liquid-feeding pumps 10, 14 controls a liquid-feeding amount (an amount of liquid to be fed) by controlling a number of revolutions of a motor. The liquid-feeding flow paths 2, 4 are merged by a mixer 18. The mixer 18 mixes the mobile phases A and B to be fed into a flow path 20 for analysis. A separating column 24 is provided through an injector (sample injecting section) 22 in the analysis flow path 20. A detector 26 is provided in downstream of the separating column 24.
A sample injected from the injector 22 is led to the separating column 24 by the mobile phases mixed by the mixer 18, and separated into respective constituents. The separated constituents of the sample are detected by the detector 26.
The liquid-feeding amounts of the liquid-feeding pumps 10, 14 are respectively controlled by a control device 19a so that the liquid-feeding amounts are changed according to a certain liquid-feeding program.
Using such a liquid chromatograph, as seen from FIG. 5A, an analysis is started from a liquid-feeding state in which a percentage of the mobile phase A liquid is 100% and a percentage of the mobile phase B liquid is 0%. Then, concentration of the mobile phase A liquid is gradually reduced whereas concentration of the mobile phase B liquid is gradually increased. Eventually, the percentage of the mobile phase A liquid is changed to 0% and the percentage of the mobile phase B liquid is changed to 100%. Thus, the sample is analyzed while a retention amount of the sample in the column 24 is changed. Such analysis is called a gradient analysis method. Particularly, the gradient system in which the plurality of the liquid-feeding pumps is used and the plurality of the mobile phases is merged on the downstream side of the liquid-feeding pumps is called a high-pressure gradient system (for example, refer to JP-A-2003-98166) . In FIGS. 5A and 5B, A and B in the vertical axis represent that the percentage of A liquid is 100% and the percentage of B liquid is 100%, respectively. The horizontal axis represents time.
In the related mobile phase supplying apparatus having the configuration shown in FIG. 4, for example, in the liquid-feeding state in which the percentage of the mobile phase A liquid is 100% and the percentage of the mobile phase B liquid is 0% before the start of the analysis, or in the liquid-feeding state in which the percentage of the mobile phase A liquid is 0% and the percentage of the mobile phase B liquid is 10%, one of the two liquid-feeding pumps 10 and 14 on a side in which the percentage of the mobile phase is 0% remains in a drive-stopped state. In a general gradient analysis, before the start of the analysis, the state at this time (in this case, the liquid-feeding state in which the percentage of the mobile phase A liquid is 100% and the percentage of the mobile phase B liquid is 0%) is maintained for a while so as to stabilize a state in the separating column 24.
Assuming that in the state before the start of the analysis, the percentage of the mobile phase A liquid is 100% and the percentage of the mobile phase B liquid is 0%, while the state before the start of the analysis is maintained, airtightness in the liquid-feeding pump 14 which remains stopped cannot be completely maintained. Thus, the mobile phase A liquid on the liquid-feeding side is pushed out toward the liquid-feeding pump 14, which causes a back-flow of the mobile phase A liquid. When an amount of the back-flow is large, even when the liquid-feeding pump 14 starts to feed the liquid after the start of the analysis, the mobile phase B liquid is not fed for the amount of the back-flow at first. Thus, as shown in FIG. 5B, arise of the gradient is poor, and accurate analysis cannot be performed. The same also applies to the case where in the state before the start of the analysis, the percentage of the mobile phase B liquid is 100% and the percentage of the mobile phase A liquid is 0%.